Shooting a wire over a grove of tall trees. What works?
The canon worked pretty well after a lot of "revisionizing" of the
design. I now have a 1000ft inverted V antenna. I runs on the tops of
the trees and is stretched to the very tip top of my 80ft tower on the
hill top. The coax runs about 400 ft through the woods to the Western
terminus of the V. To give a counter poise I ran three 120ft radials
from the starting point of the coax and the V. It probably needs more
radials but it doesn't need as many as a 1/4wave vertical because the
driving point impedance is about 10x greater than the vertical. So I
have a home brew 500ohm to 50ohm transformer at the driving point to
match the coax. It loads up with a less than 1.8:1 SWR from 1.8 MHz
to 29MHz. It is slightly directional to the East according to NEC
simulations.
Running this antenna was fraught with frustration. I used 4lb test
line shot from the canon. Missing was frequent and that light line
would be blown by the wind into trees that it shouldn't be in. The
line would often break before getting the job done requiring redoing.
I did pull 40lb test before pulling the insulated wire. The wire is 8
#22 conductors in a grey UV resistant ribbon.The antenna wire got
stuck in the guys of the tower a number of times requiring climbing
the tower 3 times. (That reminds me I have one guy on the tower
currently disconnected.) It seemed that the whole project was fighting
me tooth and nail.
It works though. I used it in the CQ 160M CW contest this weekend. I
couldn't stay up very late being exhausted from building the antenna
so I only worked about 6 hours total over two evenings. Made 115
contacts. I'm not so hot at CW. I can answer a CQ OK but if I call CQ
I get all panicked and fail to operate especially when three guys
answer at once at 35 WPM.
Bob Brunius
|